Recently, environmental problems on global scale are gathering keen attention. In also coating industry, attempts for environmental improvement are positively advanced. In particular, most of volatile organic solvent (VOC) is discharged during coating steps and effective countermeasure is of urgent necessity. With the view to reduce VOC discharge, conversion of paint in general to water-based type is being advanced.
However, conventional water-based paint generally is inferior in coating film performance such as mechanical properties and water resistance, as compared with solvent-based paint.
While it is generally effective for improving coating film performance to use high molecular weight resins (in particular, acrylic resin), there is a problem that use of, for example, intraparticulate crosslinking type high molecular weight acrylic resin emulsion degrades finished appearance such as coated surface smoothness, and coating workability.
On the other hand, JP 2004-137504A discloses aqueous acrylamide polymer solution having a specific concentration and weight-average molecular weight of 500,000-10,000,000 at a specific viscosity range, as an aqueous high molecular weight polymer solution. The main use of the polymer, however, is for paper reinforcing agent. It is unsuitable for use in paint, because it shows unsatisfactory finishing property and coating workability as a high molecular weight acrylic resin for paint use, and coating film formed thereof has insufficient water resistance.